I was messing around on cracked.com and found this very funny tidbit. Any of you remember the konami code? (Also known as contra-code or 30 lives code)

From the wiki:

Created by Kazuhisa Hashimoto, who was developing the home port of the 1985 arcade gameGradius, a scrolling shooter released on the Nintendo Entertainment System in 1986. Finding the game too difficult to play through during testing, he created a cheat code to give the player a full set of power-ups (normally attained gradually throughout the game). The code was present in the released Gradius after Kazuhisa forgot to remove the code.

It is still present today in numerous games and even websites. Even here, really! try it!